The present invention relates to a device for the regulation of air flow through secondary, tertiary, and quartenary combustion air ports of a chemical recovery boiler.
Pulp for papermaking is typically manufactured according to the Kraft process wherein wood chips are treated with a chemical cooking liquor. The wood chips and liquor are cooked in a digester under predetermined pressure and temperature conditions. At a subsequent point in the process, a xe2x80x9cblack liquorxe2x80x9d, comprising spent chemicals and organic material, is separated from the pulp and is processed in a chemical recovery boiler for reclaiming the cooking chemicals.
This xe2x80x9cblack liquorxe2x80x9d is the fuel for the recovery boiler. It is spray injected into the firebox of the recovery boiler through several nozzles that are located several meters above the boiler floor. The xe2x80x9cblack liquorxe2x80x9d is atomized during injection, dries and falls to the floor of the boiler, forming a mound called the char bed. The xe2x80x9cblack liquorxe2x80x9d has both organic and inorganic constituents wherein the organic constituents burn at a high temperature, and the inorganic constituents are reduced within the char bed to a molten state. The inorganic constituents of the xe2x80x9cblack liquorxe2x80x9d are the cooking chemicals that are being reclaimed. The char bed may exceed two meters in depth with its shape and size controlled by jets of combustion air flowing from the primary and secondary air ports. When the char bed grows in size so as to reach the elevation of the secondary ports, these air jets enhance the localized combustion and xe2x80x9cburn backxe2x80x9d that area of the char bed thus controlling the height and shape of the char bed. The tertiary and quartenary ports, if present, reside at a higher elevation, introduce the rest of the combustion air, and create turbulence to promote mixing, combustion and heat release in the boiler. Some older boilers have just primary and secondary air ports, wherein the secondary air ports correspond in location and function to the tertiary ports mentioned above.
The mass flow control of the combustion air through the ports is critical as it must be controlled to remain within certain stoichiometric parameters, as well as perform the functions discussed above. If not, the overall efficiency of the boiler decreases and mechanical problems abound. Since it is difficult to completely mix the fuel and combustion air, it is common practice to add more combustion air than required for stoichiometric conditions. This helps promote complete combustion. If too much air is admitted to the boiler, however, it will cause an excessive vertical gas flow in the boiler which entrains more particulates and pushes the heat release higher in the boiler causing increased fouling on heat exchanger components and decreased thermal efficiency. Since the air ports affect the lateral and vertical gas flows in the boiler, the location, quantity, and size of the air jets is a critical factor in their performance, in addition to the mass flow of air admitted. Herein lies the problem.
Some boilers have secondary ports that are positioned too high for optimal control of the bed height or are designed such that they require excessive air flow to accomplish this task. If the char bed gets too high it is hard to control and the core may be too cold to properly recover the inorganic constituent. It is also often the case that there are too many secondary ports and/or the ports may be too small. Conversely, many boilers have oversized secondary ports to take into account the fouling that causes a reduction to their opening size until they can be cleaned manually with steel rods. A further difficulty is that other boilers have poor tertiary or quartenary port performance wherein the air jets do not interact optimally with the gas flows and require excessive amounts of air to accomplish the mixing, combustion and heat release functions. A further disadvantage is that some boilers have air ports that do not allow the air to penetrate very far into the boiler, and therefore do not enhance combustion of the fuel. Finally, many newer boilers utilize an apparatus to regulate the air flow through the air ports, however this apparatus is generally structurally fixed to the air port, requires adjustment prior to cleaning of the airport, and is notoriously unreliable. The air ports in a boiler are fixed in location. Once they are made, they cannot be moved to accommodate changing needs or peculiarities of operational characteristics of a given boiler.
In the prior art, nozzles have been inserted into air ports, to provide a more concentrated air jet out of the port. However, adding the nozzles raises space considerations in the duct work around the ports. Reducing the free space around the port can affect the air flow characteristics in the ducts and makes installation of additional equipment problematic.
The above mentioned problems with the lackluster performance of the existing prior art air ports causes operational inefficiencies such as excessive down time, low quality inorganic constituent recovery, slow xe2x80x9cblack liquorxe2x80x9d burn rates, excessive fouling on boiler surfaces, poor thermal efficiency and poor char bed control.
In accordance with the present invention, an air port damper is provided which is adapted to regulate the mass flow and direction of a combustion air jet stream into a boiler. It is an object of the present invention to alleviate the above problems by providing an apparatus and method to control the direction of the air jets as well as the mass flow through the ports. For example, if the secondary ports are located too high, the secondary air jets can be angled downward, such that they interact with the char bed at the optimal height.
In a preferred embodiment, the air port damper is an apparatus that contains a louvered system (for controlling the direction of the air jet through an air port), a damper system (for regulating the mass flow of air through an air port), and an mechanism for moving the air port damper apparatus into or away from its operational position.
It is accordingly an object of the present invention to provide an improved apparatus for adjusting the direction of a combustion air jet stream into a boiler.
It is another object of the present invention to provide an improved apparatus for regulating combustion air into a boiler.
It is a further object of the present invention to provide an improved tool that in effect allows a boiler operator to xe2x80x9cmovexe2x80x9d the ports of the boiler by altering the air flow characteristics therethrough.
It is still another object of the present invention to provide a method of controlling the direction and flow of combustion air into a boiler through an air port that does not interfere with the on-line cleaning of the boiler.
It is yet a further object of the present invention to provide an improved method of controlling char bed height in a boiler.
It is still a further object of the present invention to provide an improved method for reducing internal boiler fouling.
It is another object of the present invention to provide an apparatus capable of separately regulating the mass air flow and adjusting the direction of air flow into a boiler through its existing air ports.
It is another object of the present invention to provide an improved apparatus capable of separately regulating the mass air flow and adjusting the direction of air flow into a boiler through its existing air ports, while working in conjunction with an automatic port cleaner.
It is another object of the present invention to provide an improved apparatus capable of separately regulating the mass air flow and adjusting the direction of air flow into a boiler through its existing air ports such that the total mass airflow required may be reduced.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.